This invention relates to a horseshoe which taken in combination with a horse's foot imparts a conformance resembling that commonly found in healthy active unshod horses living in a natural environment.
Further, the invention relates to a horseshoe which has the ability to flex about at least one articulation point to assume a desired shape and width. In addition, the invention relates to a horseshoe which includes a resilient pad for attenuating shock and vibration associated with impact events.
Horseshoes have been used for centuries in order to afford protection to the horse's foot and to enhance performance. Most horseshoes in use today are made of metal such as steel, aluminum alloys, and rarely, stainless steel or titanium. Aluminum alloys are most commonly used today in racing as such are characterized by relatively low weight and expense. Horses engaged in training or racing are commonly reshod every two to three weeks. This is done in consideration for the wear incurred by the horseshoes, but also by the desire to maintain healthy geometry with respect to the configuration of the foot and so facilitate optimal biomechanics, or way of going.
Alternatively, horseshoes are also made from various plastic, rubber, or composite materials. However, plastic, rubber, or composite horseshoes have not substantially replaced more conventional metal horseshoes in the marketplace. This is largely due to the existence of outstanding questions or problems regarding the durability, weight, expense, biomechanical soundness, or possible adverse health effects associated with such horseshoes. In particular, the use of some plastic materials and/or the adhesives used to bond a plastic horseshoe to a horse's foot have sometimes led to illness, as these materials can release chemicals which are capable of migrating or diffusing into the horse's foot.
Non-metallic materials such as plastic or rubber are sometimes used in combination with a metal horseshoe and such hybrid products are generally referred to in the industry as bonded horseshoes. Examples of bonded horseshoes include, e.g., U.S. Pat. No. 4,889,188 granted to William H. Anderson on Dec. 26, 1989, U.S. Pat. No. 5,320,184 granted to Alfred A. Noffsinger on Jul. 14, 1994, and U.S. Pat. No. 5,348,098 granted to Benedetto Di Giulio on Sep. 20, 1994. Plastic and rubber materials have been chemically and/or mechanically bonded to metal shoes to create various configurations, e.g., these materials have been used between upper and lower metal layers of a horseshoe, between the horseshoe and the hoof, on the ground engaging portion of a horseshoe, and to completely encapsulate a metal horseshoe.
A wide variety of pads, boots, and padding materials have also been used in order to protect horses from point loads, and the shock and vibration associated with impact events. For example, pads including honeycomb shaped cells containing a gas are recited in U.S. Pat. No. 5,509,484 granted on Apr. 23, 1996, and U.S. Pat. No. 5,289,878 granted on Mar. 1, 1994, to Curtis L. Landi and Susan L. Wilson. This technology has been commercialized and is known and sold under the HONEYCOMB PAD trademark. Further, a horse can sometimes become injured by incorrect shoeing, disease, or trauma during exercise. Pads which teach the provision of support for the center of the foot and frog in order to relieve the loads being placed upon various tendons and the coffin bone or P1 include, e.g., U.S. Pat. No. 4,878,541 granted to Palle Pedersen on Nov. 7, 1986, and U.S. Pat. No. 4,775,011 granted to David B. McCuan on Oct. 4, 1988. Therapeutic horseshoes for supporting the frog, tendons and coffin bone also include, e.g., U.S. Pat. 5,439,062 granted Aug. 8, 1995, and U.S. Pat. No. 5,253,715 granted Oct. 19, 1993, to Eugene D. Ovnicek.
Like the majority of conventional plastic or rubber bonded shoes, most pads or boots serve to elevate the horse's foot above the ground support surface over and above the height of a conventional horseshoes. Conventional horseshoes commonly range in height approximately between 0.18-0.375 inches. Higher foot elevations can be associated with increased instability, faulty biomechanics and greater risk of injury. Further, increases in shoe weight possibly coupled with higher foot elevations and resulting biomechanical changes can also lead to injury by taxing the horse's joints, muscles, tendons and ligaments. This is especially true with respect to athletic horses which commonly run at speeds exceeding 30 miles per hour, as the terminal velocity of the distal portions of the horse's limbs can then be moving at several times that speed.
The surfaces on which horses train and perform also vary widely. Horses frequently train and compete on grass, sand, cinder, crushed stone, and sometimes on packed surfaces which nearly approach the hardness of asphalt or cement. The hardness of the training or racing surfaces can greatly increase the effective rate of loading, thus the shock and vibration, e.g., the peak g forces which the horse will experience. Such will necessarily influence the nature of the waveform and the primary frequencies of shock and vibration transmitted to a horse's anatomy. These factors can directly affect a horse's efficiency, athletic performance and the amount of trauma that will be experienced.
Accordingly, it can be readily understood that the potential for injury is large whenever horses train or race on hard surfaces. In this regard, knowledgeable human distance runners and coaches learned many years ago that the artificial track is a good place to perform required speed work or to compete. However, the track is an unsuitable environment for conducting the bulk of the training program lest athletes quickly become injured and mentally stale. Likewise, horses are best trained by placing them into open paddocks and training them on forgiving yet not unstable natural surfaces. Clearly, no single factor can so greatly affect the level of stress being placed upon a horse, as can the training or racing surface and overall training program.
The teachings of the present invention can be better appreciated if some of the biomechanical events associated with the phenomenon under discussion are understood. While the characteristic biomechanics or way of going of horses can vary, e.g., as between Standardbreds and Thoroughbreds, what normally happens as a horse's foot and hoof impacts the ground is that the back of the foot touches first, then the foot flattens and slides anteriorly skating across the surface. In particular, this is true of a horse's rear foot, then the rear portion of the foot is loaded and deflection takes place. This will generally cause the foot to rotate backwards at the heel. The foot will then rotate forwards and recover to a relatively neutral position. Subsequently, the foot rapidly rotates forwardly and about a rocker point located between the geometric center of the foot and a short distance behind the anteriormost area of the toe as the foot breaks over and toe-off takes place, thus ending the ground support phase and beginning the flight phase.
It is known that the foot of an active unshod horse living in a natural environment will wear such that the front and back of the hoof become gently rounded. In fact, horseshoes which are initially substantially rectangular in cross-section will wear in these areas and eventually enable the combination of a horse's foot and horseshoe to assume a somewhat similar shape. Unfortunately, many conventional horseshoes are so constructed as to require replacement by the time this more natural configuration is attained. It is also known that the hoof of an active unshod horse living in a natural environment will assume a slightly arcuate concave shape in the toe area between the medial and lateral sides, as when viewed from the front, but also along both sides of the hoof between the toe and heel. This configuration permits the hoof to better slide or plane over the ground support surface during the braking phase as impact takes place, thereby reducing the effective rate of loading and the shock and vibration experienced. Further, this configuration also permits the hoof to better grab the surface during the later propulsive phase, and to break over and make a faster transition during toe-off, thus enhancing stride frequency and exhibited speed. The ability of the horse's hoof to slide somewhat can also enhance stability relative to a situation in which a horse's foot would suddenly catch or grab the ground support surface, as can happen with the use of horseshoes having rectangular configurations which possibly further include toe grabs, raised traction members or cleats. Of course, the presence of extremely loose or slippery ground can neutralize the possible adverse effects of such traction devices, and in fact, such may provide better performance and safety in such circumstances.
However, the use of horseshoes having relatively high elevations, relatively rectangular shape in the area of the toe, or raised traction members such as toe grabs can inhibit the ability of the horse's foot to break over, that is, to rapidly toe off in the latter part of the propulsive portion of the ground support phase. This tendency is more pronounced when such devices are used on relatively hard ground support surfaces. Besides resulting in a reduction of the horse's stride frequency and exhibited speed, such can also result in excessive strain being placed upon tendons and result in serious injury, perhaps crippling a horse. U.S. Pat. No. 5,566,765 granted on Oct. 22, 1996, and U.S. Pat. No. 4,721,165 granted on Jan. 26, 1988 to Eugene D. Ovnicek, which have been commercialized, known, and sold under the WORLD RACING PLATE trademark, U.S. Pat. No. 5,368,104 granted on Nov. 29, 1994, and U.S. Pat. No. 5,165,481 granted on Nov. 24, 1992 to Dave Duckett, and U.S. Pat. No. 4,333,532 granted to Paul E. Mennick on Jun. 8, 1982, discuss the known condition of a healthy horse's foot in the natural state and teach various devices and means thought to be conducive to the maintenance of a horse's health and to provide optimal performance. All of the above recited patents are hereby incorporated by reference herein.
Furthermore, it is known that in the unshod natural state, a horse's foot and hoof will flex and slightly widen when it is loaded. Discussion of this known phenomenon is found, e.g., in U.S. Pat. No. 4,513,824 granted to Donald F. Ford on Apr. 30, 1985. The use of relatively rigid metal or aluminum horseshoe substantially prevents this natural movement and so tends to reduce both the effective size, and the shock and vibration absorbing capability of a horse's foot. A steel horseshoe is known to be more flexible in this regard than an aluminum or titanium horseshoe. It is believed that the occurrence of hoof cracks is sometimes caused by the flexing and widening action of the foot and hoof working against the nails associated with a substantially inflexible horseshoe. An object of the present invention is to provide a horseshoe that will facilitate the natural widening flexing movement of the horse's foot and hoof while still providing the protection and wear afforded by conventional horseshoes.
It is known that when shod, the downward movement of the center of a horse's foot can sometimes impact the inner upper edge of a conventional horseshoe, as such may not perfectly fit the shape of the horse's foot or otherwise accommodate for this movement. U.S. Pat. No. 5,186,259 to Stephen T. Teichman granted Feb. 16, 1993, hereby incorporated by reference herein, as well as the aforementioned patents to Dave Duckett teach the inclusion of a recessed area in the inner top surface of a horseshoe for accommodating this possible movement. The ability of the horseshoe of the present invention to flex and widen as the horse's foot is loaded can provide further accommodation for this phenomenon.
One of the challenges encountered when attempting to reduce the rate of loading, and attenuate the shock and vibration experienced by a horse is posed by the fact that a horse is a rather large animal, e.g., commonly weighing between 800-1400 pounds, and when running at speeds between 30-40 miles per hour, a load exceeding 15,000 pounds can be placed upon a horse's leg. Accordingly, approximately 2600 pounds per square inch can be placed upon a typical horseshoe having roughly 6.5 square inches of working surface. When running on a hard race track, the entire duration of the impact event can be as short as 1.5 milliseconds, and over 350 peak g's can then be experienced, as illustrated in U.S. Pat. No. 4,565,250 granted to Kent Vasko on Jan. 21, 1986, hereby incorporated by reference herein. By way of comparison, humans commonly experience something in the range of only 10-14 peak g's of acceleration when running on asphalt in quality athletic footwear. By way of comparative anatomy, the most distal bone proximate the horse's hoof, i.e., the coffin bone or P1, corresponds to the most distal phalange in the tip of the finger or toe of the human hand or foot. All things considered, it is perhaps surprising that equine injuries are not more common.
The magnitude of the loads commonly placed upon the horseshoe, as discussed above, tends to prohibit the use of soft plastic, rubber, or other elastomeric and resilient materials, as used in athletic footwear made for human use which are commonly in the range between 35-55 Shore Asker C durometer. The loads placed upon the horse's foot and hoof are such that most pads or bonded shoes in the prior art have utilized materials having a Shore A hardness in excess of 75, and generally in the range between 85-95 durometer, e.g., see the pad taught in U.S. Pat. No. 3,747,684 granted to Bjorn Valter Wallen on Jul. 24, 1973. Otherwise, the stiffness of the plastic or rubber material proves insufficient to prevent substantial deformation which could result in an unnatural hoof angle, bottoming out of the material, or an inefficient spring rate, and thereby possibly induce injury. As previously discussed, pads which greatly elevate the foot can also induce instability and injury. Further, the indiscriminate use of large quantities of relatively heavy plastic or rubber material having a high durometer is not an efficient means of reducing the rate of loading, and attenuating shock and vibration. Moreover, the use of a large surface area of elastomeric material such as rubber adjacent the hoof, and in particular, when such is sandwiched between the horse's hoof and a metal horseshoe, as shown, e.g., in U.S. Pat. No. 3,861,472 granted to Edward McConnon on Jan. 21, 1975, commonly results in the metal shoe squirming about and working against the heads of nails until one or more nails actually become severed and the horseshoe works loose. This is a relatively common experience with athletic horses engaged in training and competition and can result in the crippling of a horse. Accordingly, it can be advantageous to avoid the introduction of a large surface area of relatively soft plastic or rubber material adjacent the hoof.
The present invention serves to reduce the rate of loading, and attenuate the shock and vibration which is experienced by a horse when running. It can be advantageous to provide a resilient pad which serves as a spring and dampener to reduce the normal rate of loading and unloading by extending the duration of these events over time. Further, the spring rate of the resilient pad and amount of deflection provided thereby can be engineered as to provide tuned and efficient mechanical response characteristics relative to the known biomechanics of a horse having a given approximate body weight, running style and velocity. Unlike the majority of prior art horseshoes including a pad, the present invention teaches introducing a pad in such a manner as to not further elevate the foot substantially beyond the height of a typical conventional horseshoe. Further, the present invention teaches the use of a pad which is substantially disposed in the rear portion of a horseshoe. The loading experienced in the rear portion of a horseshoe is sudden and primarily associated with impact during the braking phase, and loading of the foot during stance, whereas the loading which is experienced in the anterior portion of the horseshoe is normally less sudden and largely associated with the propulsive phase. It can then be readily understood, that the introduction of a resilient pad in the anterior portion of a horseshoe which would deflect when loaded could result in reduced efficiency and speed without providing substantial benefit as concerns shock and vibration reduction.
Yet another aspect of vibration reduction and isolation concerns the duration to which a sentient being such as a human or a horse is subjected to vibration due to an impact event. When a metal bell is struck the bell will resonate and continue to ring for an extended time while the vibration energy is gradually dampened out. The same thing is true with regards to a metal horseshoe. When horses run on hard tracks the ringing of their horseshoes can be heard at some distance. This is unfortunately frequently the case with Standardbreds which tend to strike harder with their front legs as a consequence of their running style and often run upon firm track surfaces.
The dampening capability of the horse's hoof and foot in combination with the dampening provided by the running surface will silence the ringing of the metal horseshoe over time, but due to the multiplicity of impacts, perhaps not until after the horse has finished its run. When a small bell is rung, one can place one's hand upon it and silence it. Likewise when a note on a piano is played, the vibrating metal string can be dampened by the felts incorporated into the piano's mechanism.
The use of felt pads between metal horseshoes and the horse's hoof tends to accomplish the same task.
An example of a felt pad is taught in U.S. Pat. No. 5,137,093 granted to Dennis N. Stephens on Aug. 11, 1992. But again, there can be certain problems with the use of such pads. Felt pads can absorb and retain water thereby add to weight carried at the hoof, and can also serve as a haven for minute plant and insect life. Again, most pads serve to raise the height of the horses foot above the ground and thereby inherently decrease stability.
The present invention can rapidly attenuate the vibration of a horseshoe caused by impact with a ground support surface. In particular, the present invention can accomplish this without substantially elevating or adding weight to a horseshoe. Unfortunately, horses can not talk and tell us what they are feeling when we hear their metal shoes ringing as they impact upon a hard track surface. But many of us probably have experience in using aluminum baseball and softball bats, and know that when it rings, it stings. Associated with that stinging is pain, reduced sensation and proprioception, and even reduced neuromuscular effort as the body seeks to protect itself from a perceived source of trauma or injury. This phenomenon can then result in injury and decreased performance.
A technology pioneered by Steven C. Sims, as taught in U.S. Pat. No. 5,362,046, granted Nov. 4, 1994, hereby incorporated by reference herein, has been commercialized by Wilson Sporting Goods, Inc. into the SLEDGEHAMMER.RTM. INTUNE.RTM. tennis rackets, by Hillerich and Bradsby Company, Inc. in the LOUISVILLE SLUGGER.RTM. SIMS STINGSTOP.RTM. trademark aluminum baseball and softball bats, as well as the POWERBUILT.RTM. SIMS SHOCK RELIEF.RTM. golf club line. These products substantially eliminate the ringing and stinging associated with impact events.
However, the present invention teaches another method of vibration decay time modification during and after an impact event with respect to horseshoes. Changing the effective length and geometry of a rigid member, and in particular, changing the effective length and shape of a horseshoe with the use of relatively inflexible or rigid segments which are substantially interrupted or isolated by areas of relatively flexible and resilient dampening material can dramatically affect the characteristic mode(s) of vibration and nodal points of a horseshoe. The negative nodal point is a point at which a substantial portion of the vibration energy in the horseshoe will pass as the horseshoe is excited by the energy associated with an impact event. Discussion of modes of vibration and negative nodal points can be found in Arthur H. Benade, Fundamentals of Musical Acoustics, 2nd edition, New York: Dover Publications, 1990, Harry F. Olson, Music, Physics and Engineering, 2nd edition, New York: Dover Publications, 1967, and U.S. Pat. No. 3,941,380 granted to Francois Rene Lacoste on Mar. 2, 1976, this patent hereby being incorporated by reference herein.
In a preferred horseshoe of the present invention, the characteristic mode(s) of vibration and nodal points are so altered, and the dampening material is introduced in such a manner as to substantially prevent the horseshoe from going into resonance and ringing during and following an impact event.
An object of the present invention is to provide a horseshoe which does not substantially elevate the horse's foot above the height of conventional metal horseshoes, thus minimizing the possible introduction of instability.
An object of the present invention is to minimize the amount of plastic or rubber material which is placed in communication with the horse's hoof in order to reduce the amount of expose of the hoof to possible migration of substances contained in such materials which could adversely affect the health of the horse's foot. Further, an alternate object of the present invention is to use plastic and rubber materials which are known to be relatively harmless and not subject to such degradation.
An object of the present invention is to avoid placing a large surface area of resilient plastic or rubber material sandwiched between a metal horseshoe or like component and a horse's hoof, as such is known to result in squirming of the horseshoe, damage to the nails, and perhaps catastrophic loss of a horseshoe during training or racing.
An object of the present invention is to avoid the addition of weight to a horseshoe, as such can cause greater trauma to joints and connective tissue, and alterations in a horse's biomechanics or way of going which can be inefficient and result in interference.
An object of the present invention is to reduce the effective magnitude of the loads, and shock and vibration, and also the vibration decay time associated with the use of horseshoes.
An object of the present invention is to provide something resembling the conformance and performance which the active horse's foot acquires in the natural unshod condition to a foot which is shod with a horseshoe.
An object of the present invention is to facilitate the natural flexing and widening of the horse's foot when weight bearing.
An object of the present invention is to provide a therapeutic horseshoe/pad combination for possible use with injured horses.
An object of the present invention is to provide a horseshoe having at least one articulation point so that the horseshoe can be flexed in order to assume a desired shape and width and thereby be easily fitted to a horse's foot.
An object of the present invention is to provide a simple and effective shape and width adjusting device for use with a horseshoe of the present invention.